Microchannels have been formed on non-permeable substrates such as semiconductor substrates, sapphire substrates, and glass substrates. The microchannels are able to be used in microfluidic devices that can have many different functionalities. For example, microfluidic devices have been used for air sampling for environmental monitoring and bodily fluid delivery for biosensing applications, to name a couple. Additionally, the microchannels may be used for thermal management applications on the substrate, such as liquid cooling. However, these applications currently cannot be implemented on packaging substrates. Microchannels are not currently possible in packaging substrates because they require a channel that completely seals the fluid within the channel from the organic dielectrics used as build up layers. When the fluid is not completely sealed, the organic dielectric material will absorb some of the fluid being delivered through the microchannel. Absorption of the fluid can result in performance degradation of the microfluidic device and potential package failure (e.g reliability problems, delamination between layers, etc.).
Furthermore, current packaging substrate manufacturing processes cannot produce completely sealed channels because the interconnect vias and other features are formed in the dielectric layers with laser drilling processes. Due to laser limitations, these features can only be circular holes or discontinuous lines which are later plated to produce vias. Accordingly, features fabricated with laser patterning are not able to create continuous walls that can form the channel. Additionally, the current laser drilling operations rely on a plating operation that is not capable of forming the hollow channel interiors that are needed to allow for the fluid to flow.
Thus, improvements are needed in the area of packaging substrate fabrication in order to form microchannels.